1. Field of the Invention
This invention relates to the production of molds for producing investment castings of titanium and similar metals and alloys.
2. Description of the Prior Art
It is known in the metal working art to employ coatings on molds and dies to reduce reactivity between the metal being treated and the mold or die material. This is shown for example in U.S. Pat. Nos. 2,806,271 which shows deposition on the mold surface of a metal film of the metal to be cast; 3,177,084 which shows the application of a carbide layer to graphite forging dies; 3,537,949 which describes layered shell mold in which the first layer comprises a powdered nonreactive metal and subsequent layers of ceramic and 3,680,626 which describes the use of a surface layer of a boron containing ferrous material in the casting of aluminum articles. U.S. Pat. No. 3,180,632 describes a graphite mold for casting titanium and the provision of a rare earth oxide layer on the mold surface.
U.S. Pat. No. 3,494,997 describes a ceramic mold which is produced with a binder composed of heterogeneous metal alcoholates. These alcoholates presumably decompose upon firing. The prior art relating to the investment casting of titanium is described in the booklet "Investment Casting of Refractory Metals" by Mueller and Koon, published in 1972 by Rem Metals Corporation, Albany, Oregon. This booklet discloses that it is known in the prior art to use tungsten molds in the casting of titanium and that such molds produce superior castings. The mold production method described involves a first layer of tungsten powder and binder with subsequent layers of ceramic material and binder.